If a transformer has more turns on its secondary than the primary, it is a

• A. Step up transformer
• B. Step down transformer
• C. Isolation transformer
• D. Autotransformer

Answer: (A)

Voltage in a transformer is determined by the turns ratio: Vs/Vp = Ns/Np. When the secondary winding has more turns than the primary, this ratio is greater than one, so the secondary voltage rises above the primary voltage. That behavior is what defines a step-up transformer. In an ideal case, power stays the same, so the increased voltage on the secondary comes with a reduced current there (Is = Ip × Np/Ns). The other options describe different purposes or configurations (isolation, or using a single winding with taps), but the clear consequence of more turns on the secondary is that the device steps the voltage up.